The control of foam formation is crucial in many industrial processes such as paper manufacture, waste water treatment and latex paint formulation. In particular, in the manufacture of latex paint, many of the additives required may themselves contribute to foam formation. Surfactants and dispersants are necessary to stabilize both the binder resin and the pigment in the latex. However, these surfactants also stabilize foam under the dynamic conditions of mixing and shear required in the formulation process. Other components such as leveling agents and coalescing aids may also contribute to foam formation. Due to the large effect that additives can have on the final coating properties, a critical requirement for any compound added for foam control is that it must be effective at low concentration. It also must not impart undesirable characteristics to the final coating surface such as fish eyes or pinholes.
When referring to foam control in aqueous systems, it is recognized that there are two separate and distinct phenomena involved. One is the elimination or reduction of existing foam, often referred to as “foam knockdown.” Agents or compositions that function in this manner are referred to as defoamers. The other situation that must be considered is the prevention of foam formation in aqueous systems when they are subjected to dynamic conditions such as shear. Agents or compositions that function to prevent foam formation are referred to as antifoams. It is often the case in many industrial aqueous systems that both types of activity are required. In other words, it is often necessary to eliminate existing foam while simultaneously preventing the generation and stabilization of additional foam as the aqueous system is subjected to dynamic conditions. It is often the case that an agent or composition that accomplishes one function will not necessarily accomplish the other. In other words, a composition or agent that is effective in the knockdown of foam may not be effective in preventing the generation and stabilization of foam as the aqueous system is further subjected to dynamic conditions. Thus, an agent or composition that can function as both a defoamer and an antifoam is highly desirable.
The ability of the foam control agent to also function as a wetting agent is also highly desirable. In aqueous systems such as latex paints and waterborne inks, wetting agents such as surfactants and dispersants must be added to wet and stabilize pigment particles in the formulation. Foam control agents that can simultaneously function as wetting agents are highly desirable since fewer additives may be required to achieve the same performance in a particular formulation. The ability of foam control agents to simultaneously function as wetting agents also greatly reduces the likelihood that they will contribute to surface defects once the coating or ink formulation has dried.
Numerous classes of compounds and mixtures of compounds have been utilized for foam control in latex paint formulation. Silicones and silica particles dispersed in the oil phase of a water in oil emulsion are known to be effective in suppressing foam in aqueous systems. However, when utilized as foam control agents in latex paint manufacture, many of these silicon-based compounds and dispersions are known to impart undesirable effects to the final coating due to their incompatibility. Other known foam control agents including vegetable and mineral oils, and polyethers of alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide have been disclosed such as those disclosed in U.S. Pat. No. 4,836,951. Another class of molecules that are known to suppress foam formation in aqueous systems are acetylenic diols and alkane diols such as those disclosed in U.S. Pat. No. 6,762,208. In particular, the acetylenic diol 2,4,7,9-tetramethyldecyne-4,7-diol (TMDD) sold by Air Products Corporation under the trademark Surfynol 104® is widely utilized in aqueous systems.
More recently alkyl glycidyl ether adducts of diamines and polyamines have been disclosed in U.S. Pat. No. 6,746,623 and U.S. Pat. No. 6,656,977 as effective foam control agents. The preferred compositions found to be most effective at controlling foam formation were the 2:1 adducts of 2-ethylhexyl and isobutyl glycidyl ether with diamines and polyamines. No examples of adducts of diamines or polyamines with alkyl epoxides were disclosed.
We have now discovered that alkylene oxide derivatives of diamines and polyamines in which the alkylene oxide is a C4 to about C24 alkylene oxide are more effective foam control agents than the corresponding glycidyl ether adducts and thus represent a substantial improvement over the prior art. We have also discovered that when such alkylene oxide adducts of diamines and polyamines are neutralized, they not only suppress the formation of foam under dynamic conditions but also may simultaneously reduce or eliminate existing foam in such aqueous systems. We have further discovered that such alkylene oxide/amine adducts also reduce the dynamic surface tension thus providing the additional benefit of wetting in such systems. Moreover, to our knowledge, alkylene oxide adducts of diamines or polyamines in which the alkylene oxide contains four or more carbon atoms have not been previously reported in the literature and are thus novel compositions. These inventive compositions are liquids at normal use temperatures and thus are more easily handled than solid materials.